You can use both the free and the premium version of Yousician with your students.
The free version is a great risk-free way to try Yousician, and see how it works for you and your students. Their practice time will be limited, but during their initial session they'll receive feedback on accuracy and timing, earn stars etc.
The big advantage of the premium version is that practice time is unlimited. So, students who pay for Yousician can practice as much as they like, and spend the time they need to improve quickly, refine their skills, and build mastery. As you know, learning an instrument requires countless hours of effort and attention, and Yousician premium helps make the journey engaging, motivating and rewarding.